In order to guide an aircraft along its flight path, it is known to use a navigation system that enables the computation of navigation data including the longitude position and the latitude position of the aircraft. Other navigation data such as the bearing, the speed, and the route of the aircraft can also be computed by the navigation system.
This navigation data can be used by systems such as the flight management system (FMS) or the flight control and guidance system (FCGS). The systems using this data enable the aircraft to be guided along its flight path as a function of the navigation data.
Navigation data can be transmitted between the navigation system and the system using the data using different communication means, such as the ARINC 429 bus or the AFDX™ network.
For improved accuracy, it is known to format each longitude or latitude position datum on two words. Thus a first word is used to encode a numerical value corresponding to a coarse component of the position datum, while a second word is used to encode a numerical value corresponding to a fine component of the position datum.
The two words are then combined with each other, for example by the flight management system or the flight control system to reconstruct an accurate value of the latitude or longitude position that is required.
To limit the consumption of computation resources, the coarse component of the position datum may be computed at a frequency lower than that at which the corresponding fine component is computed.
For example, the navigation center may compute the fine component of a position datum every 10 ms and compute the coarse component of that position datum every 20 ms.
FIG. 1 shows a time scale t on which are represented fine components LF1, LF2, LF3, LF4 computed every 10 ms and coarse components LC1 and LC3 computed every 20 ms. It is then apparent that for the second cycle of computation of the fine component, the associated coarse component has not been computed.
In fact, the coarse component that follows the coarse component LC1 is computed at a time t corresponding to the third cycle of computation of the fine component.
Using the FIG. 1 diagram again, FIG. 2 shows the cyclic operation of computation of the position datum by an arrow RCS1, RCS2, RCS3. This operation corresponds to combining at the end of a cycle of computation the fine component and coarse component pair computed for this cycle. Each pair of components is designated by a brace.
The computation by the system using the latitude or longitude position datum for the second cycle may then include an error.
An object of the present invention is to make it possible to compute accurately the longitude and/or latitude position datum of a moving craft for a given cycle of computation of a fine component of the position datum when the corresponding coarse component has not been computed over this cycle.